The present invention relates to a cathode ray tube display mounted in a television set or the like, and a television set having the same, and more particularly to a cathode ray tube display having a screen aspect ratio of 16:9 and a television set having the same.
Cathode ray tube (hereinafter referred to as "CRT (Cathode Ray Tube)") displays used in television sets or the like have been recently designed in a wide size, and this wide-size design has promoted the spread of CRT displays having screens whose aspect ratio is 16:9 (hereinafter referred to as "16:9 CRT displays (or screens)") together with conventional CRT displays having screens whose aspect ratio is 4:3 (hereinafter referred to as "4:3 CRT displays (or screens)").
A television set having a CRT display of aspect ratio 16:9 as described above (hereinafter referred to as "wide television") is designed so that in several kinds of picture (display) mode users can watch pictures which comprise frames of an aspect ratio 4:3 of the conventional NTSC system (hereinafter referred to as "4:3 pictures").
These picture modes include a normal mode in which a 4:3 picture is directly reproduced on a 16:9 screen (a screen having an aspect ratio of 16:9) as shown in FIG. 1A, a zoom mode in which a 4:3 picture is displayed on the 16:9 screen so that the lateral frame length of the 16:9 screen is made the same as the lateral length of the 4:3 picture and upper and lower portions of the 4:3 picture which protrude from the 16:9 screen in a vertical direction are trimmed as shown in FIG. 1B, a wide mode in which the 4:3 picture is enlarged on the 16:9 screen and the protruding upper and lower portions of the picture are compressed in the vertical direction of the screen as shown in FIG. 1C.
There is also known a television having a scroll mode in which a user can freely scroll the picture to watch upper or lower portions protruding from the 16:9 screen in the vertical direction when the zoom mode as described above is set.
In general, time information or the like which is displayed at the top of the screen, for example, in a morning or evening time range, is trimmed when the zoom mode is set, and it obstructs information supply to a user. The scroll mode as described above enables the scrolling of pictures in the vertical direction, so that a trimmed picture portion can be also displayed on the screen.
Accordingly, at the present time when pictures are displayed on a screen while enlarged (reduced), trimmed or the like, when an user watches on a wide television having a 16:9 screen video software of 4:3 aspect ratio which are respectively formed in the screen (display) modes as described above, it is necessary to optimally adjust both the frame size in the vertical direction and the picture position in the vertical direction for each of the respective software every time. In such a wide televisions, the adjustment of the frame size in the vertical direction has been hitherto performed by adjusting the amplitude of a vertical deflection (scan) waveform signal (VSAW), and also the adjustment of the vertical picture position has been performed by adjusting the DC component of the vertical deflection waveform signal (VSAW) or making the vertical linearity non-linear.
FIG. 2 is a circuit diagram showing a deflection system of the CRT display mounted in a wide television, for example.
In FIG. 2, reference numeral 21 represents a synchronizing separation circuit, and it serves to separate a vertical synchronizing signal (V.SYNC) and a horizontal synchronizing signal (H.SYNC) from a video signal (CVBS) which is supplied from a pre-stage circuit of a television set (not shown), and then output the separated vertical and horizontal synchronizing signals. Reference numeral 22 represents a count-down processor which comprises a counter or the like. The count-down processor 22 is normally reset by the vertical synchronizing signal, and it counts the horizontal synchronizing signal. For example, even when the vertical synchronizing signal (V.SYNC) output from the synchronizing separation circuit 21 is missing, the count-down processor 22 is reset with the same period as the vertical synchronizing signal to generate position information S of the vertical frame.
Reference numeral 23 represents a vertical deflection waveform generator which outputs a vertical deflection waveform signal (VSAW) which has been adjusted on the basis of the position information S of the vertical frame supplied from the count-down processor 22. Reference numeral 24 represents a horizontal deflection correcting waveform generator which outputs a horizontal deflection correcting waveform signal (E/w) to adjust the horizontal deflection waveform signal on the basis of the position information S of the vertical frame supplied from the count-down processor 22.
Reference numeral 25 represents a control circuit comprising a microcomputer or the like, and it outputs a control signal to control respective parameters of the vertical deflection waveform generator 23 and the horizontal deflection correcting waveform generator 24 as described below.
The operation of the CRT display shown in FIG. 2 will be described with reference to the output waveform of each part shown in FIGS. 3, 4A and 4B.
The synchronizing separation circuit 21 separates a vertical synchronizing signal (V.SYNC) and a horizontal synchronizing signal (H.SYNC) from a video signal (CVBS) which is supplied from an earlier stage circuit (not shown), for example, and supplies these signals to the count-down processor 22. The count-down processor 22 generates and outputs the position information S of the vertical frame in conformity with the period of the vertical synchronizing signal (V.SYNC) shown in FIG. 3 on the basis of the vertical synchronizing signal (V.SYNC) and the horizontal synchronizing signal (H.SYNC). Further, the position information S of the vertical frame can be represented by s=Kt at each period of the vertical synchronizing signal (V.SYNC) where s represents an instantaneous value for representing a frame position with a time (K represents a coefficient, t represents time).
The position information S of the vertical frame is supplied to the vertical deflection waveform generator 23 and the horizontal deflection correcting waveform generator 24. For the instantaneous value s of the vertical frame position information S, the vertical deflection waveform generator 23 outputs the vertical deflection waveform signal (VSAW) adjusted according to the following function equation (1): EQU VSAW:v(s)=B(Cs.sup.3 +Ds.sup.2 +s)+A (1)
where A: parameter to adjust vertical frame position
B: parameter to adjust vertical frame size
C, D: parameters to adjust vertical linearity
That is, if the value of each parameter is set to satisfy C=D=0 and B=1, the vertical deflection waveform signal becomes v(s)=s+A, and thus the frame is vertically scrolled in conformity with the value of the parameter "A". Further, the zoom mode display can be performed on the basis of the value of the parameter "B", and the linearity of the display frame can be corrected by the parameters "C", "D" and "B".
On the other hand, the horizontal deflection correcting waveform signal (E/W) which is calculated by a function equation (2) shown below for the instantaneous value s of the position information S of the vertical frame (a signal to correct the horizontal deflection waveform signal) is output from the horizontal deflection correcting waveform generator 24 to form a horizontal deflection waveform signal whose linearity has been corrected with the above signal. EQU E/W: u(s)=F(Gs.sup.4 +s.sup.2 +Hs)+E (2)
where E: parameter to adjust horizontal frame size
F: parameter to correct horizontal pin distortion
G: parameter to correct horizontal corner pin distortion
H: parameter to correct horizontal trapezoidal distortion
Here, it will be assumed that in the normal mode in which pictures of aspect ratio 4:3 are directly reproduced on a CRT display of a wide television having a screen aspect ratio of 16:9, a control signal with which the values of the respective adjustment parameters "A" to "D" of the function equation (1) are set to "A.sub.1 ", "B.sub.1 ", "C.sub.1 " and "D.sub.1 " is output from the control circuit 25 and the vertical deflection waveform signal (VSAW) with which an image having no distortion on the screen as shown by a chain line in FIG. 4A can be obtained is output from the vertical deflection waveform generator 23.
For example, when pictures are required to be enlarged in the zoom mode, the value "B.sub.1 " of the parameter B for adjusting the vertical frame size in the function equation (1) above is set to "B.sub.2 " on the basis of the control signal from the control circuit 25, and the amplitude of the vertical deflection waveform signal (VSAW) is varied as indicated by a solid line in FIG. 4A, whereby the vertical frame size is adjusted.
Further, when the pictures are scrolled in the vertical direction in the scroll mode, the value "A.sub.1 " of the parameter A for adjusting the picture position of the vertical frame in the function (1) is set to "A.sub.2 " on the basis of the control signal from the control circuit 25, and the vertical deflection waveform signal (VSAW) indicated by a chain line of FIG. 4B is shifted, for example, in the upward direction as indicated by a solid line in FIG. 4B, whereby the picture position of the vertical frame is adjusted.
Accordingly, by inputting the vertical deflection waveform signal (VSAW) and the horizontal deflection correcting waveform signal (E/W) to an output drive circuit in a later stage (not shown), horizontal and vertical deflection currents providing frames whose linearity and picture position on the screen are corrected can be generated and a picture whose linearity has been corrected has been finally displayed.
The vertical deflection current which is output in each screen mode of the wide television described above is set to one of the waveform current signals shown in parts (a) to (c) of FIG. 5. The upper part (a) of FIG. 5 shows the waveform of the vertical deflection current in the normal mode, the middle part (b) of FIG. 5 shows the waveform of the vertical deflection current in the zoom mode, and the lower part (c) of FIG. 5 shows the waveform of the vertical deflection current in the wide mode. Each vertical deflection current waveform in FIG. 5 is assumed to be linear to make understanding easy.
As is apparent from FIG. 5, the waveform of the deflection current in the zoom mode shown in (b) of FIG. 5 is increased by about 25% as compared with the waveforms of the vertical deflection current in both the normal mode and the wide mode because the amplitude of the vertical deflection waveform signal (VSAW) in the zoom mode is increased by about 25% as compared with the other screen modes.
However, paying attention to any one point in the vertical direction within the effective frame of the wide television as shown in FIG. 5, a one-to-one (1:1) corresponding relationship exists between any point and the vertical deflection current irrespective of the screen mode. Therefore, when the start point of the trace of the vertical deflection current is considered to be a start time, the time until the vertical deflection current reaches a specific value differs depending on the screen mode, and therefore the time period from the start time until a scan position reaches any one point on the screen differs in accordance with the screen mode.
A large number of wide televisions and other types of television which can display various parameters of currently-used functions (brightness, tone, etc.) on the screen have been recently put on the market. In order to display the parameters of the respective functions, a microcomputer built in a wide television monitors the current status of the screen mode and calculates a time period from the start time until the scan position reaches any one point on the frame to output a timing pulse together with the parameter information, whereby the parameters are displayed in the same positions on the screen.
As described above, the adjustment of the vertical frame size and the adjustment of the picture position of the vertical frame are performed by controlling the parameters "B" and "A" of the function equation (1) of the vertical deflection waveform generator 13, however, this adjustment work causes some distortion in the linearity of the vertical deflection waveform signal (VSAW) with respect to the vertical position of the frame and the horizontal pin cushion of the horizontal deflection correcting waveform signal (E/W).
Therefore, the values of all the parameters "A" to "H" of the function equation (1) for adjusting the vertical deflection waveform signal (VSAW) and the function equation (2) for correcting the horizontal deflection correcting waveform signal (E/W) for adjusting the horizontal deflection waveform must be adjusted again to correct the distortion of the vertical linearity and the horizontal pin cushion every time the adjustment of the vertical frame size and the position adjustment of the vertical frame are carried out.
In a CRT display of a wide television or the like in which the time period from the start time of the vertical synchronizing signal until the display time of the frame differs in accordance with the screen mode, when the frame is scrolled with the scroll mode to vary the picture position in the vertical direction under the zoom mode, a time period until the scan position arrives at any point in the vertical direction cannot be covered by merely setting some wait times, and each of the wait times must be calculated on the basis of the data of the screen mode. Therefore, a large load has hitherto been imposed on the software of the microcomputer.
In order to solve the above problem, there has also been proposed such a countermeasure that the horizontal synchronizing signals are digitally counted with the period of the vertical synchronizing signals and the calculation of the wait time which has been performed according to the software of the microcomputer is performed by using a deflection system circuit. However, from the viewpoint of the precision of an interface, the counting frequency must be set to several times as high as the horizontal synchronizing signal, and thus the cost rises.
Further, a deflection yoke in the vertical direction must be driven beyond the effective frame in the zoom mode, and thus reflection of electron beams may occur. Therefore, it is necessary that blanking is applied to video signals to avoid the reflection of the electron beams, and some restriction has had to be imposed on the output of the vertical drive circuit to avoid an undesired load from being imposed on the deflection yoke driving circuit. However, since the necessary video blanking time varies in accordance with the screen mode as described above, the setting of the video blanking is very troublesome
In the case of limitation of the deflection current, if a limiter is merely provided in the vertical drive circuit, the output of the vertical drive circuit itself would fluctuate due to the adjustment as a result of dispersion of the CRT or the deflection yoke driving circuit, and consequently it has not been possible to obtain a sufficient effect.